Nylon spun bonded fabric-concrete composite

ABSTRACT

A high-impact resistant concrete-spun bonded fabric laminae including a layer of concrete and a planar fabric comprised of continuous nylon filaments arranged without apparent order within the plane of the fabric and being autogenously bonded together at a substantial number of touching filament crossover points, the fabric being at least partially embedded and under tension in said concrete.

United States Patent Gothard et al. 1451 Jan. 25, 1972 [54] NYLON SPUNBONDED FABRIC- 3,509,010 4/1970 Metzger ..161/162 CONCRETE COMPOSITE3,531,367 9/1970 Karsten l6l/l60 [72] Inventors: Edwin S. Gothard, Cary;John D. Calfee, FOREIGNPATENTS R APPUCATlONS bmh 1,125,663 8/1968 GreatBritain 161/151 [73] Assignee: Monsanto Company, St. Louis, Mo.

OTHER PUBLICATIONS [22] Filed: June 8,1970

Fibrous Reinforcement for Portland Cement from Modern PP N04 44,492Plastics, by S. Goldfein, April, 1965, pages 156- 158.

Primary Examiner-William A. Powell [52] U.S.Cl..161/140,l6l/l50,l61/l5l,

, 161/157, 161/170, 264/71, 264/228, 264/333 stt;mey-(.il.NBolwnl,11l3lss,Jr., Russell E. Wemkauf, John D. 51 1111.01. ..B28b 23/04, B32b13/02, B32b 13/14 P am ea [58] Field of Search ..l6l/57, 59,140, 146,I48,

161 150,151,157,159, 162, 168-l70,402; [57] ABSTRACT /7 52/309 Ahigh-impact resistant concrete-spun bonded fabric laminae including alayer of concrete and a planar fabric comprised of References continuousnylon filaments arranged without apparent order within the plane of thefabric and being autogenously bonded UNITED STATES PATENTS together at asubstantial number of touching filament cros- 1,379,s37 5/1921 Ruppel..161/269 ux Sever Points, the fabric being 311938! Partially embeddedand 2,332,703 10/1943 Elmendorf ..161/157 undertension in said Concrete-2,473,528 6/1949 Hoover ..161/269 X 3,336,179 8/1967 Campbell et al ..l6l/72 8 Drawmg F'gms PAIENTEU JINZSIIIYZ K IMPACT FORCE STATIC SUPPORTSTATIC SUPPORT FIG. I.

PREPARE CONCRETE RECIPE PREPARE MOLD- WET SPUNBONDED NYLON FABRIC PLACEWETTED FABRIC IN BOTTOM OF MOLD COVER FABRIC WITH CONCRETE RECIPE CURECONCRETE INVENTORS JOHN D. CALFEE EDWIN S. GOTHARD PIC-3.3.7

ATTORNEY NYLON SPUN BONDED FABRIC-CONCRETE COMPOSITE BACKGROUND OF THEINVENTION 1. Field of the Invention This invention relates to a cementconcrete composite having a greatly improved impact strength, thecomposite consisting of a layer of spunbonded fabric adhered to theconcrete in the area in which the concrete is under tensile stresses.

2. Description of the Prior Art It has been recognized that the lowtensile strength of concrete severely limits its applications. In thepast, attempts to compensate for the lack of tensile strength inconcrete has usually involved either unstressed reinforcing steel rodsor prestressed reinforcing steel rods. However, neither of theseprocedures really overcomes the low tensile strength limitation butmerely bypasses it for any concrete structure which has a region intension is subject to have cracks form and propagate through that regionin tension. Such cracks form at relatively low stresses and continueeither until they reach a free surface or until they reach a region thatis in compression. When concrete is subjected to blast forces producingshock and vibration, it will most likely be destroyed unless reinforcedby an extensive steel complex. This reinforcement, however, does notprevent the concrete from shattering and causing extensive damage.

Furthermore, the tensile strength exhibited in conventional reinforcedor plain concrete, as calculated by standard tests, cannot be reliedupon for design purposes since small incipient cracks due to fatigue,thermal shocks or cavities cannot be detected. Such crack formations andthe subsequent propagation thereof are not always present but theconditions favorable for their existence cannot always be predicted.Even the exercise of exceptional control procedures does not eliminatecrack formation and growth. It has long been accepted that aboutone-half of the material in a normally reinforced concrete beam isuseless to resist tensile loads. The detrimental effects of tensioncracks in reinforced concrete beams are not limited solely to loss ofload-resistant area. For example, it is apparent that tension crackingseverely limits the effectiveness of concrete tanks for containingliquids. Likewise, the wrapping of pipelines with concrete results inthe addition of little load-bearing value.

U.S. Pat. No. 3,429,094, to Romualdi teaches the incorporation of shortlinks of straight steel wire in the concrete recipe. The steel wireprovides the two-phase material with a crack-arrest mechanism thatincreases cracking strength and provides toughness to the degree allegedunattainable in conventional concrete. However, in the Romualdi patent,crack retardation is provided only by the high modulus wirecounteracting the stresses ahead of the crack. While such is anadvantage, the Rornualdi two-phase concrete is incapable of turning thecracked plane so that the crack both multiplies and takes a torturouspath through the material which substantially increases the energyneeded to propagate the crack. Further, steel wire basically does notreadily adhere to the concrete and is easily pulled out upon precedinglow impact energies. The surface characteristics of the wire can bealtered to improve adhesion such as by providing flattened areas;however, the flattened areas reduce the volume fraction of wire in theconcrete which can be achieved by using round, smooth, wire.

SUMMARY OF THE INVENTION This invention is a composite structurecomprised of a spunbonded nonwoven fabric lamina and a concrete laminawhich are adhered together at least along their contiguous surfaces by afabric lamina being at least partially embedded in the concrete lamina.The nonwoven fabric lamina is comprised of continuous nylon filamentswhich are arranged in the plane of the fabric without apparent order.The nylon filaments do not have a lubricant coating or other type offinish so that the adhesion of the nylon to the cement is enhanced. Thenylon filaments comprising the fabric lamina are autogenously bondedtogether at a substantial number of touching filament crossover pointsto provide multidirectional stability. The array of filaments isadaptable to alter the direction of travel of the crack plane throughthe material so as to divide and subdivide its path thus increasing theenergy needed to propagate the crack. Autogenously bonded" means thatthe bonds between the filaments are formed in the absence of an externabinder for the reason that binders may not withstand the alkalinity ofthe concrete. For example, two filaments may be autogenously bondedtogether by the application of heat in that the fibers are fused at thecrossover points. Autogenous bonding also includes the use of solventssince upon the removal of the solvent from the filament, the polymerscomprising the filaments are mixed at the filament crossover points.However, the preferred method for autogenously bonding nylon filamentsis by the use of a hydrogen halide gas, and more specifically, hydrogenchloride gas. The filaments absorb the hydrogen chloride gas along thesurface areas which results in the breaking of the intermolecularhydrogen bond between adjacent amide groups. Upon desorbing the hydrogenchloride gas from the nylon filaments, the intermolecular hydrogen bondbetween amide groups of different fibers reform resulting in bonding atthe interfilament crossover points. As a byproduct of hydrogen chloridegas bonding, the hydrogen chloride gas etches the surface of the nylonfilaments so that the filament surface area is substantially increased.it is thought that the increased surface area aids in the mechanicalbonding or the adherence of the nylon filaments to the concrete,

The concrete recipe is generally comprised of cement, sand, aggregateand water. However, the concrete recipe may include strength increasingmaterial such as chicken wire, short steel wire and nylon staple fibers.While the spunbonded nylon fabric as described herein may cover morethan one surface, it must be contiguous with the concrete lamina alongthe concrete laminas surface subjected to the maximum tensile stresses.While one or more spunbonded nylon fabric lamina may be embedded adistance from the surface having the maximum tensile stresses, it hasbeen found that the fabric is most efficacious when it comprises thesurface of the concrete lamina receiving the maximum tensile stresses.

While the filaments comprising the fabric may be completely undrawn,partially drawn, completely drawn, it has been found that partiallydrawn and undrawn nylon filaments are more effective in increasing theenergy required for postcrack separation. The reason is thought to bethat upon the development of a crack, the nylon filaments must be colddrawn to the completely drawn state before rupture of the filamentsoccurs, such drawing consuming tremendous amounts of energy.

In preparing the composite of this invention, the nylon spunbondedfabric must be applied to the cement recipe while the fabric is in awetted and elongated state. Upon being exposed to water, nylon expandsor grows from 1 to 6 percent. Thus, the total surface area of thespunbonded nylon fabric will also increase by a proportional amount, forexample, from 2 to 12 percent. Upon drying, the fabric will try toreturn to its original area. If the fabric were associated with theconcrete recipe prior to being expanded by water, the moisture in theconcrete recipe would cause the fabric to expand, thus creating bulgesand ripples along the surface. Therefore, by associating wetted nylonspunbonded fabric with the concrete recipe, the fabric will inherentlytend to return to its original state upon the curing of the concrete andthe drying of the fabric, but is prevented from completely doing so bythe hardening of the concrete. By the failure of the fabric to return toits original at rest state, the fabric is maintained under a tensionwithin the concrete which aids in the dissemination of the crack plane,when developed, throughout the composite. Also, the concrete adjacent orproximate to the fabric is under slight compression, the extent to whichthe fabric is under tension.

Therefore, an object of this invention is to provide a concrete articlewhich is reinforced with nylon spunbonded fabric along the exteriorsurfaces of the concrete receiving the maximum tensile stress.

Another object of this invention is to provide a concrete spunbondednylon fabric laminae which is exceptionally resistant to high impactforces.

Another object of this invention is to provide a concrete spunbondedfabric laminae in which the fabric is adhered to the concrete and inwhich the fabric is under tension.

These and other objects of this invention will become apparent when thedetailed description is read in conjunction with the drawings.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a section taken through a typicalconcrete-nylon spunbonded fabric laminae showing the fabric lamina beingadhered to the concrete lamina along the side being subjected to thetensile stresses;

FIG. 2 is a greatly enlarged schematic view of the spunbonded nylonfabric showing the fiber arrangement with the fabric and showing thefilaments dividing the crack plane into a multiplicity of directions;and

FIG. 3 is a block diagram illustrating the process of this invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Substantially allpolyamide fibers may be used to form the spunbonded fabrics of thisinvention. Nylon 6, nylon 4 and nylon 6,6 are especially adaptable dueto their affinity for water. For simplicity, the nylon subsequentlyreferred to is nylon 6,6 which is prepared by condensing hexamethyleneadipamide and adipic acid. Spunbonded nonwoven fabrics may be made bymany processes, one of which being set forth in US. Pat. No. 3,338,992.The melt extruder is used for spinning continuous nylon filaments. Theformed filaments are then drawn downwardly away from the extruder by anaspirator which also deposits the filaments by means of moving air on aconveyor belt. The nylon filaments comprising the fabric are bondedtogether at a substantial number of filament crossover points by beingpassed through a chamber containing an activating gas, such as, hydrogenchloride. The nylon filaments absorb the hydrogen chloride which rendersthem bondable upon the removal of the gas. Thus, the filaments arepermanently bonded together at their touching crossover points bydesorbing the gas from the filaments by either being subjected to heator by being passed through a water bath. While the web just described iscomprised completely ofnylon filaments, other continuous filaments maybe incorporated into the web which are not subject to attack from thecements alkalinity such as, for example, polypropylene and polyethylene.However, the incorporation of other filaments which do not have theaffinity for water as compared to nylon, results in the fabric having areduced contractive force upon being dried. To fully illustrate thisinvention, the spunbonded nonwoven fabric as herein described iscomprised wholly of nylon filaments.

The concrete recipe is generally comprised of cement, sand, aggregateand water. Other strength-inducing materials may be added such as staplewire and the like. The order of mixing found most efficient includes theplacing of the course aggregate in the mixer while it is in operationafter which the sand, cement and then water are added in that order. Themixer is generally allowed to run at least 5 minutes after allingredients have been added.

Both wooden and metal molds may be used to form the specimen. Generally,a Saran-(polyvinylidene chloride) type liner is placed in the mold andallowed to have sufficient overhang to permit complete enclosure of thespecimen. The Saran insures moisture retention and acts as amold-releasing agent. To insure a flat surface for receiving the nylonspunbonded fabric, a thin sheet of acetate may be placed on top of theSaran. With the mold being prepared to receive the nylon spunbondedfabric, the fabric is thoroughly wetted and placed smoothly in the moldon the acetate sheet. The mold may then be placed on a vibrating tablewhich is operated during the filling cycle and until a smooth surface isformed on the concrete. Where opposed surfaces of the composite may besubjected to tensile stresses, as for an example in a highway medianstrip which is placed between oncoming lanes of traffic, a second laminaof nylon spunbonded fabric may be wetted and placed on the top surfaceand troweled until all air pockets are removed.

Curing is accomplished by leaving the mold containing the respectiveingredients at room temperature at least for 24 hours after which thesame is subjected to atmospheric pressure steam in a curing chamber.After remaining in the steam chamber for at least 24 hours, the mold isremoved and is allowed to be cooled down to room temperature beforetesting.

In reference to FIGS. 1 and 2, composite 20 is comprised of concretelamina 22 and nylon spunbonded fabric lamina 21 with fabric 21 being atleast partially embedded in concrete 22 so that adequate bonding betweenthe laminae is achieved. For purposes of illustration, composite 20rests on the static supports and is provided with an impact force. Atthe moment of impact, moiety A of concrete lamina 22 is under acompressive stress while moiety B is under a tensile stress which placesfabric 21 under the greatest tension since fabric 21 represents thepoint being furthest from line C" which is the neutral layer ofunstressed material. Assuming that in fabric 10 a crack plane developedalong filament 11 at its termination point, the crack plane would bepropagated along that filament to filament junction 12 where it would bedivided and propagated along the filaments comprising the junction. Withthe crack plane having been partially dispersed at junction 12, aremaining portion thereof is propagated along filament 11 to filamentjunction 13 where the crack plane is again divided and propagated alongthe filaments comprising that junction. This process is repeated untilthe crack plane is completely dissipated. By such crack dissipation,large fissures which would extend through the concrete to rupture thesame are prevented from forming. For the system to be operative, thefilaments must readily adhere to the concrete, must be continuous sothat the crack plane will be endlessly propagated and must be bondedtogether at a substantial number of touching filament crossover pointsto provide fabric integrity.

EXAMPLE I This example serves as a control. The concrete recipe wascomprised of the following:

cement6.65 pounds;

sand-2l.58 pounds;

96-inch aggregate l 2. l 8 pounds;

water 3.84 pounds.

The recipe was prepared at room temperature in a tumbletype 1.3-cubicfoot capacity mixer. The order of mixing was as follows: place courseaggregate in mixer while mixer was operating, add sand, then cement andthen the water. The mixer was allowed to run for 7 minutes after allingredients were deposited therein. A 6 by 6-inch metal mold was used toform the specimen. A Saran sheet was placed in the mold and was allowedto have sufficient overhang to permit complete enclosure of thespecimen, insuring moisture retention. A smooth acetate sheet was thenplaced on top of the Saran to insure a fiat planar bottom surface.

The mold was placed in a laboratory-size vibrating table and wasvibrated during the filling operation until a smooth surface was formedon the concrete recipe. The specimen remained in the mold at roomtemperature for 26 hours after which curing was completed by having thespecimen remain in a steam chamber for 24 hours. The steam chambercontained saturated steam at a pressure of 5 p.s.i.g. After the curingperiod, the specimen was removed from the steam chamber and allowed tocool to room temperature before testing. The resulting specimen samplewas 6 by 6 by 3!; inch thick.

The impact strength of the specimen was tested by dropping a 5.35 poundweight having a bullet-shaped nose from different heights so as to givethe impact force in foot pounds at an increasing force until initialfailure and, ultimately, total failure occurred. Initial failure iswhere a first crack is detected in the specimen and total failure, orcomplete destruction of the specimen, is considered to be a -inch bow inthe specimen in the vertical direction. The total foot pounds of forcenecessary for initial or total failure is the sum of the drops to reachthese points and the preferred order of progression is as follows: 3, 3,4, 5, 5, l0 and foot pounds.

The specimen was supported in a frame having a 41-inch thick hard rubbergasket which eliminated surface irregularities. The unsupported area ofthe specimen was 20.25 square inches. The weight was dropped from anelectrically triggered mechanism which is centered over the specimen.

The testing of this sample resulted in an initial failure of 3 footpounds and a total failure of 3 foot pounds, the initial and totalfailure being identical since the cracked plane was propagated throughthe specimen.

EXAMPLE 2 The concrete recipe used in this example was the same asprepared in example 1. A Saran-type sheet was placed in the bottom of a6 by 6 inch mold, upon which was placed an acetate sheet to insure asmooth bottom surface. The nylon spunbonded fabric which weighted 3.0oz./yd. and made as previously described was immersed in water andallowed to remain 1 minute so that fabric expansion occurs whereupon itwas placed while in a wetted condition on the acetate sheet. The moldwas then placed in the vibrator and filling occurred to a depth ofthree-fourths inch. The composite was cured in accordance with example1.

Testing of the composite after curing in accordance with example showedan initial failure of 6 foot pounds and a total failure of 40 footpounds.

EXAMPLE 3 The procedure as set forth in example 2 was repeated with theexception that the nylon spunbonded fabric had a weight of 1.0 ounce persquare yard. Testing of this composite sample showed that the initialfailure was 6 foot pounds and total failure was 10 foot pounds.

Thus, when comparing example 3 with example 2, it is shown that higherfabric weights result in a substantially greater total failure strengthdue to the increased number of filaments available to disperse thecracked plane and dis tribute the load.

What is claimed is: v

1. A composite comprised of a spunbonded fabric lamina and a concretelamina being bonded together along the concrete-fabric interface, saidspunbonded fabric lamina at least being present on the exterior surfaceof said concrete lamina positioned to receive a tensile stress, saidspunbonded lamina being comprised of continuous nylon filaments arrangedwithin the plane of the fabric and being autogenously bonded together ata substantial number of touching crossover points. 7

2. The composite of claim 1 wherein said nylon filaments are arrangedwithin the plane of said fabric without apparent order, said filamentsbeing free of surface coatings.

3. The composite of claim 1 wherein said spunbonded fabric lamina isunder tension.

4. The composite of claim 1 wherein said filaments are at least onlypartially drawn.

5. A process for forming a spunbonded fabric-concrete compositecomprising the steps of:

a. preparing a spunbonded nylon fabric;

b. preparing a concrete recipe;

c. aqueously wetting said fabric;

d. associating said wetted fabric with said concrete recipe;

and

e. curing said concrete recipe.

6. The process of claim 5 wherein said fabric is under tension aftersaid concrete recipe has cured.

7. The process of claim 5 wherein said wetted fabric is placed in a moldand said concrete recipe is deposited thereon.

8. The process of claim 5 wherein said nylon filaments are at last onlypartially drawn.

2. The composite of claim 1 wherein said nylon filaments are arrangedwithin the plane of said fabric without apparent order, said filamentsbeing free of surface coatings.
 3. The composite of claim 1 wherein saidspunbonded fabric lamina is under tension.
 4. The composite of claim 1wherein said filaments are at least only partially drawn.
 5. A processfor forming a spunbonded fabric-concrete composite comprising the stepsof: a. preparing a spunbonded nylon fabric; b. preparing a concreterecipe; c. aqueously wetting said fabric; d. associating said wettedfabric with said concrete recipe; and e. curing said concrete recipe. 6.The process of claim 5 wherein said fabric is under tension after saidconcrete recipe has cured.
 7. The process of claim 5 wherein said wettedfabric is placed in a mold and said concrete recipe is depositedthereon.
 8. The process of claim 5 wherein said nylon filaments are atlast only partially drawn.